Does anyone know if lenses have ever been made with focal lengths in excess of 6 00mm (24") with a maximum apeture less than 2" or so? Most modern lenses in the range of 30-35" are F/9-12, which makes them too heavy for field work.

Tony Brent

8-Sep-1998, 01:57

When you recall that the f number of a lens is the ratio between its diameter an d its focal length, you begin to see why a 16" f/4.5 lens would have to be consi derably bigger, heavier and bulkier than a f/4.5 8" lens.

For the first case, 4.5 diameters would have to fit in 16". For the second, 4.5 diameters would have to fit in 8". Much smaller piece of glass.

This doesnt even start to touch on the correction needed for such a big glass.

Alan Gibson

8-Sep-1998, 05:12

Tony: interesting answer, but Jack wants a small lens, not a large one. An apert ure less than 2" on a 24" lens means an aperture smaller than f/12. I'm afraid i t looks as if no-one knows. Perhaps the answer, as with so much of LF, is "hire a pack mule".